In an animated sequence, there is a series of images showing changes in subject position/pose, and/or in background, foreground or other features. For each image, there are multiple frames of drawings. Without the aid of computer animation, each frame of a given image must be redrawn. The process of redrawing each frame is tedious and time consuming.
A computer can be used to generate frames of animated drawings. Instead of drawing each frame in the animated sequence, a fewer number of key frames are actually drawn by hand or other means. Then the computer generates the necessary intermediate frames between pairs of the initial key frames to form the animation sequence. This is known as "in-betweening".
Generally, the computer generates in-between drawings using interpolation techniques on point data in an initial key-frame drawing and in a final key-frame drawing. A method of in-betweening using interpolation is described by Poggio and Brunelli in U.S. patent application Ser. No. 07/819,767. To be successful, each point on the initial drawing must be matched to a corresponding point on the final drawing. In computer animation, it is necessary to correspond control points of the initial and final key-frame drawings so the computer can interpolate between the key frames.
Matching every point between two drawings by hand is feasible when there are only a small number of control points. As the number of control points increases, the task becomes more complex and error-prone. If the drawings are matched incorrectly, then any in-between drawings generated will be incorrect.
Accordingly, there is a need for improvement in generating frames of an animation sequence, and in particular, in "in-betweening", i.e., generating in-between/intermediate drawings between given key frames.